The present invention pertains to an applicator for delivery of the proper dosage of Mitomycin C to eye tissues with a subconjunctival space created during glaucoma filtering surgery. Mitomycin C is an anti-neoplastic drug which also has a potent anti-scarring property that is highly desirable for glaucoma surgery. For the surgery to be successful, the surgically created subconjunctival space should remain open, so that an aqueous eye fluid called aqueous humor can continuously drain out through a surgically created opening through the eyeball wall. However, there is a tendency for the body to heal any wound by scar tissue formation at the wound, and this will gradually close the subconjunctival space. When the space becomes totally blocked, the eye fluid can not drain out, and the surgical correction fails. Mitomycin is used as an antimetabolite to prevent this scarring and closure of the drainage opening.
A brief description of the anatomy of the eye is in order, here made with reference to FIG. 1. The cornea 2 is the transparent front part of the eye which continues in to the white wall of the eye, the sclera 4. The colored part of the eye is the iris 6. The space between the cornea 2 and the iris 6, the anterior chamber 16, is filled with aqueous fluid. The much smaller space posterior to the iris is the posterior chamber 14. The root of the iris is attached to the ciliary body 10, which has many finger-like projections centrally, called the ciliary processes 12. The ciliary processes 12 secrete the aqueous fluid, and also project cobweb filaments to anchor the lens 24 in place. The cornea 2 and iris 6 converge to form the filtration angle wherein multi-layer sieve-like filters are located, referred to as trabecular meshworks 20.
There are pathways within the eye for aqueous humor circulation. With reference to FIG. 2, the ciliary processes 12 continuously secrete the aqueous humor, which keeps the eyeball distended and round, like air in a tire. The aqueous humor flows out to posterior chamber 14; then passes through the pupil 18 to the anterior chamber 16, thence to the trabecular meshworks 20 and into the Schlemm canal 22, and eventually out through outflow channels to the vein and systemic circulation. The amount of fluid introduced into the eye should equal the amount of fluid drained out. If the aqueous fluid leaving the eye is less than that introduced, the retained fluid will gradually build up pressure in the eye, similar to the effect of pumping more air into a tire to create a higher tire pressure. High eye pressure causes progressive nerve damage, and if not treated, eventual blindness. Medical treatment consists of using eye drops to lower the eye pressure. When medical therapy fails to lower the pressure, surgery is indicated.
In glaucoma there is too much aqueous fluid retained in the eye due to blockage in the filters and flow out vessels of the eye, causing elevated pressure.
Referring to FIG. 4, glaucoma corrective surgery involves forming an opening at the limbus 32 (cornea scleral junction) under a conjunctival flap, so that the fluid can continuously drain out to a subconjunctival space 28 formed by the surgery, and be absorbed into systemic circulation. The success of the surgery depends greatly on keeping this subconjunctival space open.
In recent years, more and more glaucoma surgeries are being performed with the help of anti-scarring drugs, notably the anti-metabolite Mitomycin C. The conventional method is to soak the operative area with Mitomycin solution using a completely saturated piece of sponge held in the space for few minutes. The operative area is then copiously rinsed with a saline solution to remove excess Mitomycin. This method of application has many inherent disadvantages. Firstly, the amount of the drug applied and absorbed by the tissues is excessive and uncertain as the volume of fluid flowing out from the easily compressed sponge is usually excessive and is not readily controlled or predicted. This procedure is thus mostly a matter of guesswork.
Secondly, there is a lack of consistency. Too little drug absorbed by the tissues will cause early surgical failure, and too much delivered will cause many serious complications due to the toxicity of the drug.
Thirdly, it is difficult to accurately apply the drug to the areas of the surrounding tissues which need to be treated.
Thus, the results are erratic and unpredictable.
If the subconjunctival space becomes blocked by scarring, which is the body's natural process of healing, the fluid can not drain out, and the surgery fails to correct the problem.
The object of the deliver invention is to provide an applicator which can present the proper dosage of an anti-scarring drug, i.e., Mitomycin C, for absorption by the tissues at the proper locations, with great consistency, to thus improve the rate of success for this type of surgery.